In transceivers, receivers and transmitters may share common components (e.g., antennas, front end units, etc.) and/or have limited isolation from each other. For effective wireless communication, transmitted signals need to travel long distances and, accordingly, require emitting relatively high power at the antenna of the transceiver. On the other hand, received signals may have traveled long distances and have much weaker power compared with the transmitter at the shared antenna. Due to the power disparity between transmitted and received signals, the transmitted signal that leaks into the receiver often imposed design challenges on the shared components as well as the rest of the receiver in order to achieve performance requirements. One example is higher order product caused by the transmitter leakage appearing at the receiver that may decrease the sensitivity of the receiver.
A Full-Duplex (FDD) direct-conversion transceiver adopted an external inter-stage filter between the low-noise amplifier (LNA) and first mixer at the receiver to help mitigate the transmit signal coming through as leakage from a design specified isolation limited duplexer. The object of this external inter-stage filter was to ease the linearity requirements of the quadrature mixer after the LNA, which compounds the challenge by amplifying the transmit leakage. Proliferation of wireless bands forced designers to adopt high linearity mixer design methodology to remove the usage of external inter-stage filters by relying just on existing duplexer design. Such a receiver design is currently adopted in most commercial cellular transceiver application-specific integrated circuits (ASICs) for mobile terminals in the wireless industry today. Design restricted by stringent isolation needs shouldered only by duplexer design results in significant insertion losses both to the transmitter and receiver, particularly when there is small spectrum separation between transmit and receive bands. This causes the loss of power efficiency and receiver sensitivity, respectively.
Therefore, there is a need for an improved transceiver design. In particular, there is a need for adaptive transmitter leakage cancelation in a transceiver.